The present invention relates to a novel class D amplifier with a switching control circuit.
In theory, class D amplifiers constitute a highly efficient power source for use in audio and illumination systems. Class D amplifiers normally include a pair of solid state switches sequentially driven by a transformer to produce a square-wave output.
Unfortunately, switching of such solid state devices are subject to loss of efficiency due to on-stage resistance, inherent capacitances, and the like. In addition, "shoot-through" currents place high electrical stress on the switch components and increase the amount of electromagnetic interference generation in the system.
Many variations have been proposed to class D or pulse width modulated amplifiers to solve such problems.
U.S. Pat. No. 3,294,981 describes a signal translation which converts an input level into two signals, each of a certain rate, retaining the characteristic of an input signal. The translation is intended to faithfully reproduce low level input signals for audio use.
U.S. Pat. Nos. 3,579,132 and 3,899,745 describe class D amplifiers which provide for decreased distortion by use of filters and transformer-coupled output circuits.
U.S. Pat. No. 4,015,213 shows a pulse width modulated signal amplifier which provides a proportion between the pulse width modulator signal and an input signal.
U.S. Pat. No. 4,056,786 teaches a low level class D amplifier in which all of the stored energy recovered during the nonconducting portion of the amplifier circuit is returned to the DC power supply.
U.S. Pat. No. 4,456,872 shows a current controlled two state modulation system which maintains a constant voltage output with use by a limiting amplifier.
U.S. Pat. No. 4,059,807 describes a pulse width modulated amplifier in which a pulse modulated signal is fed to a pulse amplifier and a low-pass filter. The output of a low pass filter is coupled back to a mixer which also receives an audio signal input.
U.S. Pat. No. 4,162,455 shows an amplifier system in which a pair of class D amplifiers are used together and which includes separate clock pulse trains to cancel switching frequency ripple at the common output of the two amplifiers.
U.S. Pat. No. 4,346,349 shows a class D amplifying circuit which enhances the power efficiency of a multi channel audio power amplifier. The carrier frequency of the class D amplifier is set at a low value to eliminate spurious radiation of the carrier signal.
U.S. Pat. No. 4,390,813 concerns a transformer for driving class D amplifiers which are to be used in the lighting field. Use of the class D amplifier is claimed to reduce power consumption.
U.S. Pat. No. 4,439,738 describes a class D pulse width modulated amplifier which includes circuitry for short circuiting turns on the output transformer to protect the amplifier against transients returning from the load.
U.S. Pat. No. Re. 33,333 teaches; an audio amplifier with a modulator for transforming an analog audio input signal into two complementary trains of pulse width modulated signals to drive the power switches. Certain pulses are dropped and compensated for by a distortion detection system.
U.S. Pat. No. 4,724,396 shows a digital audio amplifier for converting the onset of a clipping condition into a missed pulse in a pulse train generated from an analog signal by pulse width modulator. The analog input signal is attenuated and responsive to a voltage as a result of the clipping.
U.S. Pat. No. 4,884,183 shows a pulse width modulated control signal for use in a motor control which includes a variable frequency discontinuous mode controller and a hysteretic continuous mode controller for transition between modes.
U.S. Pat. No. 4,992,749 teaches a pulse width modulating amplifier circuit with a pair of bootstrap circuits for increasing the power voltage during periods of shortage.
U.S. Pat. No. 4,992,751 presents a digitally controlled amplifier circuit for use with an audio amplifier having phase modulated pulse width modulation. The output is used with a filter to smooth the pulse width modulated signal to and control the polarity of the switching circuit.
U.S. Pat. No. 5,014,016 utilizes a high efficiency amplifier circuit having first and second modulator circuits. The outputs of the two modulators circuits are coupled to a push-pull output bridge. This output is coupled to the load.
U.S. Pat. No. 5,077,539 describes a switching amplifier system in which the switching circuitry is responsive to a tri-state command signal.
U.S. Pat. No. 5,160,896 teaches a class D amplifier which adds a hystersis voltage source to limit the current flow to the conducting paths in the amplifier.
U.S. Pat. No. 5,117,198 teaches a MOSFET device for use in a class D amplifier. A pair of inductors are used with a diode combined with the MOSFETS to improve the life of the MOSFETS in the amplifier.
U.S. Pat. No. 5,306,986 shows a high efficiency class D amplifier in which the output is connected to the common node between switching transistors. In this way stray capacitance of the transistors is transferred to the inductance before switching.
U.S. Pat. No. 5,345,165 shows a two-state modulation system in which a hysteretic comparator receives a hystersis control signal to vary the threshold of the comparator.
U.S. Pat. No. 5,371,666 describes a current mode control apparatus using a pulse width modulator to reduce gate drive signals for driving the power output section.
U.S. Pat. No. 5,479,337 teaches a high efficiency analog power amplifier utilizing a pulse width modulation signal to operate switching devices coupled in series across a D.C. power source. Zero voltage level is impressed on each transistor through a resonant circuit to enable switching of the transistors.
U.S. Pat. No. 5,594,386 describes a class D pulse width modulator amplifier which has a current switch, a integrator, and a comparator connected in a feedback loop. United loop generates an ultrasonic frequency carrier which is employed to modulate a audio input signal.
U.S. Pat. No. 5,617,058 shows a digital switching amplifier where linearization of the power switches is accomplished by using three states.
A class D amplifier which solves the problems encountered in the field would be a notable advance in the electronics art.